Honor 8: How to keep an app from shutting down?

Hello. I have a few important apps that I'd like to keep running always. There is one application that won't stay running in the background, and I do not receive the notifications that are crucial unless the app window is open / in recently used applications.

Phone is Honor 8, with Emui 4.1. Android 6.0. I have enabled auto launch for applications by PM Plus by Huawei.

On Settings / Advanced settings / Battery manager / Protected apps this application is Protected.
On Phone Manager app / App auto-launch the settings for this app are "Launch in background". Some other apps have also "Launch with system, launch in background". (I don't know where I could enable this problem app to also "launch with system", but it doesn't seem to be a solution since I don't have to reboot my phone in order to stop getting notifications from this app.)

On Settings / Developer options / Running services / Show cached processes there is a "cached background process" for this app while it's visibly running. It disappears immediately after I've closed the app, and there's nothing else running that'd be obviously related to the app.